What is External Sulphate Attack?
External sulphate attack (ESA) is the most common type of sulphate attack and typically occurs where water or soils containing dissolved sulphates penetrate into the concrete surface. ESA damage is often superficial but, in some cases, can result in the complete disintegration of several centimetres depth of concrete.
What causes External Sulphate Attack of concrete structures?
Sulphates damage concrete primarily through expansive reactions with the cementitious materials present in the concrete.
When water or soils containing dissolved sulphates penetrate into the concrete, they react with the cement paste, leading to the formation of expansive compounds such as gypsum, ettringite, and thaumasite. These compounds exert pressure on the surrounding concrete matrix, causing it to crack, delaminate, and eventually disintegrate.
What are the signs of External Sulphate Attack of concrete structures?
Disintegration.
How can I identify External Sulphate Attack in concrete structures?
Visual survey | Non-destructive testing | Destructive testing |
How can I prevent External Sulphate Attack in concrete structures?
To mitigate external sulphate attack in concrete structures, various preventive measures can be implemented.
Firstly, optimizing the concrete mixture by using low water-to-cement ratios and incorporating supplementary cementitious materials (SCMs) like Ground Granulated Blast Furnace Slag (GGBS) or Fly Ash in place of Portland cement can significantly reduce permeability and bolster resistance to sulphate ingress.
Furthermore, the addition of mineral admixtures such as limestone powder further enhances the density of the concrete matrix, rendering it less vulnerable to sulphate penetration.
Another effective strategy involves the use of surface protection systems such as coatings, which serve as an additional barrier against sulphate intrusion. These protective coatings create a shield that impedes the ingress of sulphates, safeguarding both the concrete and embedded steel reinforcement.
Moreover, employing sulphate-resisting cements, specifically formulated to withstand aggressive sulphate environments, can provide enhanced durability and longevity to concrete structures exposed to sulphate attack. These cements contain reduced levels of tricalcium aluminate (C3A) and increased levels of calcium sulphate, which mitigate the adverse effects of sulphate exposure.
By employing a combination of these approaches, including optimized concrete mixtures, surface protection systems, and sulphate-resisting cements, concrete structures can effectively combat external sulphate attack and ensure long-term durability, even in harsh environmental conditions.
How can I repair the damage from External Sulphate Attack on concrete structures?